The fred.stlouisfed.org states that the total assets of all commercial banks in America as of 6/28/17 was $16,267 trillion dollars, of which, of that amount, as listed by federalreserve.gov the consolidated assets of the top four largest banks, which are JP Morgan Chase, Wells Fargo, Bank of America, and Citibank comes to a total of $6,991 trillion dollars or nearly 43% of those total assets in aggregate, effectively signifying that when it comes to the banking industry in America, these four banks, rather than being seen as competitors to one another, or in effect, an oligopoly, and such a concentration of monetary assets into too few hands allows these banks to virtually dominate all others and to thereby it is these banks that determine the prevailing interest rates that consumers will pay for loans such as for credit cards and mortgages, and to whom these loans will be originated for.
It takes absolutely no stretch of the imagination to recognize that when banks reach a certain size, and these banks have reached that size, that thereupon they have effectively positioned themselves that they are now, for all intents and purposes "too big to fail" for the consequences of the government putting any of these behemoths into receivership could very well topple the financial edifice as we know it, with potential catastrophic consequences for all those that bank with these institutions.
While it can be said, that size and consolidation has its place in regards to efficiency and scaling of businesses, when that size is so large as to basically dominate all other competitors, so that these chosen four, are privileged to be the favored few when working with governmental agencies and financial regulations in all of its many capacities, than these banks are able to thereby leverage up their consolidated power in which the laws created by lobbyists' influence favor these banks' preferences to such an extent, that this gives them an unfair advantage over all others that could conceivably threaten their position of power.
So too, because of this great concentration of assets in such a small number of banks, in which commercial banks in fit, form, and function, via our fractional reserve system, are able to create money by virtue of the assets that they hold, means that this monetary credit now created, allows these banks to multiple the money so deposited that this expands our money supply, not really for the greater good of the country and its consumers as a whole, but instead to leverage up their monetary assets in a manner that these banks are now able to make even more money for themselves in order to increase their stock price, their bonuses, and to thereby earn money when their leveraged bets work out, and when these leveraged bets do not, to thereby lean on the federal government and their regulators to bail them out or subsidize them in times of trouble.
The fact that these banks are consolidated into too few hands, means, in effect, that these big four banks have the power to set consumer interest rates, mortgage rates, fees, and services offered in a manner that would be considered to be collusion, and the smaller banks that so desire to compete against these large banks aren't able to effectively do so, because the cost of the money as well as logistics for these banks because they are so much smaller, costs them more, thereby as seen over the last twenty-five years, the top four banks continue to take a larger and larger piece of the banking pie, in which the consumers of such, both large and small, are nickel and dimed, day after day, all in the service of the big four to the detriment of consumers at large.